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G345U Lecture Notes, 10-6-10
Cassie Scruggs & Charis Smith
Expansion of the Universe:
 The universe began about 14 billion years ago
 At the beginning there was nothing more than a singularity
-The singularity had no space but contained all the energy the universe would ever
contain
- The energy was in the form of gamma rays
-The singularity expanded and continued to expand
-The first stars did not form until about ½ billion years after the “big bang” or initial
onset of the expansion of the singularity
Life Cycle of a Star:
 A star is ionized gas, also known as plasma, that produces energy by nuclear fusion
- A star is considered “live” if nuclear fusion is going on in the interior of the star
 The life cycles of stars produces heavy elements
- The first atoms made were H (hydrogen), He (helium), Li (lithium), and maybe Be
(beryllium) or B (boron)
Temperature Scales:
Absolute Zero
Freezing Point
Boiling Point of H2O
Kelvin
0
273
373
Celsius
-273
0
100
Fahrenheit
-460
32
212
 There is a larger difference between scales at smaller temperatures and not much of a
difference between scales at larger temperatures.
-Kelvin and Celsius are approximately equal at large temperatures
-Fahrenheit is approximately double Kelvin and Celsius at large temperatures
 When referring to the temperature of a star, we are using the photospheric temperature
 The photosphere is the first visible outer layer of a star
o 300-500km thick and 4000-8000Kelvin
 Fraunhofer lines determine the chemical composition of the photosphere.
o Darker lines determine the concentration of the element
http://astro1.panet.utole
do.edu/~ndm/ASTR4810/g0fraun.jpg
Waves:
 Waves transmit energy
- The height of the wave is the amplitude
- The length of the wave from crest to crest is the wave length
- The number of cycles/sec is the frequency
Light Spectrum:
 Light is an oscillating electric and magnetic field also called and electromagnetic radiation
 Light is the only energy source that can transmit through a vacuum
-It is self perpetuating because a disturbance in an electric field causes a magnetic field
and a disturbance in a magnetic field causes an electric field
-Visible light is in the 400-700nm range
 Visible light is in the 400-700nm range
 The shorter the wave length, the more energy is being produced
 Opaque objects emit electromagnetic
according to temperature
radiation
o Hot = deep red
o Hotter = red to orange
o Hotter Still = yellow to white
http://www.countryliving.com/cm/countryliving/images/CLX0305Guild007-de.jpg
 Blackbody Emission – “In physics, a black body is an idealized object that absorbs all
electromagnetic radiation falling on it. Blackbodies absorb and incandescently re-emit
radiation in a characteristic, continuous spectrum.”
http://en.wikipedia.org/wiki/Black_body
http://astronomy.swin.edu.au/cms/imagedb/albums/userpics/blackbody_radn_curves.png
Dilute Gases:
 Each chemical element produces its own unique set of spectral lines at specific intervals
 Gases can ABSORB parts of light, and REEMIT at a later time
 Emission Line Spectrum – “The emission spectrum of a chemical element or chemical
compound is the spectrum of frequencies of electromagnetic radiation emitted by the
element's atoms or the compound's molecules when they are returned to a lower energy
state.” http://en.wikipedia.org/wiki/Emission_spectrum
http://www.astro.bas.bg/~petrov/herter00_files/lec07_04.jpg
 Spectral lines are produced when an electron jumps from one energy level to
another within an atom
o There are specific orbits an electron can exist on
o To become “excited” an electron needs to absorb wavelengths
http://www.freewebs.com/mdreyes3/electron_1.jpg
 Hydrogen spectral lines are the most important when studying stars because stars
are composed mostly of hydrogen